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catalysts Article

The Promotional Effects of ZrO2 and Au on the CuZnO Catalyst Regarding the Durability and Activity of the Partial Oxidation of Methanol Hsiao-Yu Huang

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, Hao-I Chen

ID

and Yuh-Jeen Huang *

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Department of Biomedical Engineering & Environmental Sciences, National Tsing Hua University, Hsinchu 30013, Taiwan; [email protected] (H.Y.H.); [email protected] (H.I.C.) * Correspondence: [email protected]; Tel.: +886-3-5715131 (ext. 80812)  

Received: 2 July 2018; Accepted: 21 August 2018; Published: 24 August 2018

Abstract: The promoter ZrO2 was applied to prevent Cu crystallites from sintering over CZ (ca. Cu 30 wt.% and Zn 70 wt.%) under partial oxidation of the methanol (POM) reaction. Gold was selected to promote the performance of CZrZ (ca. Cu 31 wt.%, Zr 16 wt.%, and Zn 53 wt.%) catalyst to overcome a high ignition temperature of 175 ◦ C and CO selectivity (SCO ) (>10% at T. > 200 ◦ C). Experimentally, the deactivation rate constant of A5 CZrZ (ca. Au 5 wt.%, Cu 31 wt.%, Zr 17 wt.%, and Zn 47 wt.%) and CZrZ was 1.7 times better than A5 CZ (ca. Au 5 wt.%, Cu 31 wt.%, and Zn 64 wt.%) and CZ. The methanol conversion of CZrZ and A5 CZrZ catalysts was kept higher than 70% for 12 h in an accelerated aging process. Meanwhile, the Au prompted more methoxy species oxidizing to formate on Cu+ -rich A5 CZrZ surface at lower temperature, and also improved CO transfer from formate reacting with moveable oxygen to form CO2 . The SCO can lower to ca. 6% at 200 ◦ C after adding 3–5% of gold promoter. These features all prove that the CZ catalyst with ZrO2 and Au promoters could enhance catalytic activity, lower the SCO and ignition temperature, and maintain good durability in the POM reaction. Keywords: POM; Au Promoter; oxygen mobility; durability

1. Introduction Hydrogen as a clean energy source has been an important focus of research for more than a decade. Partial oxidation of methanol (POM), an exothermic reaction, is one of the reactions employed in producing hydrogen at low temperatures [1–3]. The low reaction temperature of POM can simplify the reactor design. In addition, the exothermic property and higher reaction rate at lower temperatures can shorten the start-up time and reach working temperatures more quickly. In addition, no heat supply is required if the reaction reaches steady-state [2,4,5]. Thus, the POM reaction is considered to be more energy-efficient than the steam reforming of methanol (SRM) reaction; thus, it can produce hydrogen affordably on an industrial scale. The POM reaction is shown as Equation (1): CH3 OH + 1/2O2 → 2H2 + CO2 , ∆H0 = −192 kJ·mol−1

(1)

Copper-zinc oxide (CuZnO) catalysts have been widely used for POM due to high methanol conversion, high H2 selectivity, and low cost. However, significantly higher CO selectivity (SCO ), higher ignition temperature (Ti) (~185 ◦ C) [3,6], and poor durability typically restrict the application of CuZnO-based catalysts [7,8]. Generally, the sintering of copper is the main factor for the deactivation of the catalyst. Thus, more-suitable promoters have been tested to improve catalyst activity and durability of CuZnO-based catalyst in POM reaction. Li and Lin [9] used Al2 O3 , MgO, and ZrO2 to

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promote the CuZnO-based catalysts in POM and found that Cu/Zn/ZrO2 performed with the slowest deactivation rate, as well as with better methanol conversion in POM. Sanches [10] indicated that the preparation methods and promoter influenced the structural and textural features of the catalyst. Compared with CuZnO catalysts prepared by coprecipitation (CP) and homogeneous precipitation (HP) methods, the CuZnO-based catalyst with Zr promoter prepared using the CP method had the highest Cu surface and lattice constant, and better methanol conversion in SRM. CuZnO-based catalysts contain ZrO2, which apparently has improved the Brunauer–Emmett–Teller (BET) surface area up to 2–3 times [10–13] and enhanced dispersion and reducibility in the methanol steam reforming (MSR) reaction [14]. In addition, the Cu-based catalysts with ZrO2 extended the Cu2 O phase after MSR reaction. The degree of Cu2 O aggregation is assumed to be smaller than Cu metal, which is expected to have better durability [15]. Amorphous ZrO2 particles, which work to stabilize the catalyst structurally and hamper the aggregation of Cu and ZnO particles, delay the deactivation of CuZnO [13,16,17]. In 1987, Au nanoparticles ( CZrZ = A5 CZrZ. The deactivation rate

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2018, 8, x FOR PEER REVIEW of 19 = CZCatalysts > CZrZ = A5CZrZ. The deactivation rate constant of A5CZrZ and CZrZ catalyst was31.7 times constant of A CZrZ and CZrZ catalyst was 1.7 times lower than CZ catalyst. Co-existence of Au and 5 lower than CZ catalyst. Co-existence of Au and ZrO does not induce negative effect in 19 the POM = CZ > CZrZ =A The deactivation constant A5CZrZ and CZrZ catalyst was 1.7 times Catalysts 8, REVIEW 33of Catalysts 2018, 8,5xCZrZ. xFOR FORPEER PEER REVIEW ofbe 19 ZrO does2018, not induce negative effect in therate POM reaction.ofHowever, optimized conditions cannot reaction. However, optimized conditions cannot be reached with the existence of only Au or ZrO. lower than CZ catalyst. Co-existence of Au and ZrO does not induce negative effect in the POM reached with the existence of only Au or ZrO.

== CZ >>CZrZ 55CZrZ. deactivation rate of was CZHowever, CZrZ== A A CZrZ.The Theconditions deactivation rateconstant constant ofA A55CZrZ CZrZ andCZrZ CZrZcatalyst catalyst was1.7 1.7times times reaction. optimized cannot be reached with and the existence of only Au or ZrO. lower lower than than CZ CZ catalyst. catalyst. Co-existence Co-existence of of Au Au and and ZrO ZrO does does not not induce induce negative negative effect effect in in the the POM POM reaction. reaction.However, However,optimized optimizedconditions conditionscannot cannotbe bereached reachedwith withthe theexistence existenceof ofonly onlyAu Auor orZrO. ZrO.

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omoter not only enhanced the affinity to adsorb CO but also increased ith CO on the catalyst surface. The SCO could be lowered to 6% at 200 the AxCZrZ catalyst produced a good catalytic performance, reduced e, and still maintained good durability in POM reaction.

16 of 19 R PEERCatalysts REVIEW2018, 8, x FOR PEER REVIEW 16 of 19 he following are available online at www.mdpi.com/xxx/s1, Figure S1: ion: (■) CZ, (●) CZrZ, (★) Au5CZrZ, and (◊) Au5CZ at 250 °C for 12 h in an of GHSV active and oxygen. Au promoter not affinity to adsorb CO but also increased The promoter not enhanced the affinity toenhanced adsorb but also increased −1 of Kh−1Au of 47.4only hThe WHSV). Figure S2:only XRD profiles CO ofthe different moveable oxygen to react with CO on the catalyst surface. The S CO could to react with CO on the catalyst surface. The S CO could be lowered to 6% at 200be lowered to 6% at 200 Z, (b) CZrZ, (c) A1CZrZ, (d) A3CZrZ, and (e) A5CZrZ. (◊) Cu, (●) ZnO. Figure °C. Based on these features, the A x CZrZ catalyst produced a good catalytic performance, reduced e features, the A x CZrZ catalyst produced a good catalytic performance, reduced ysts after calcination for 4 h at (a) 400 °C, (b) 550 °C, and (c) 750 °C. (◆) CuO, ysts 2018, 8, x FOR PEER REVIEW 3 of 19 □) ZrO2Sco -monoclinic. Figure S4: Ramangood spectra of (a) CZ, (b) CZrZ. Table andand ignition temperature, anddurability still maintained good durability in POM reaction. emperature, still maintained inand POM reaction. MeOH Figure 1. Temperature profiles of catalyst performance: (a) conversion methanol (CMeOH ),), (b)), (b) Figure 1. Temperature profiles of catalyst performance: (a) conversion of methanol (C ),(C Temperature profiles of catalyst catalyst performance: (a) ofof methanol (CMeOH MeOH ), (b) (b) Figure 1. 1.S5: Temperature (a)conversion conversion of methanol (C MeOH Figure 1.Figure Temperature profiles ofmapping catalyst performance: (a) conversion of methanol faces measured by EDS (%). Figure The EDS element profile: (a) Z > CZrZ = A 5 CZrZ. The deactivation rate constant of A 5 CZrZ and CZrZ catalyst was 1.7 times H2 CO selectivity of hydrogen (S), ), (c) selectivity ofof carbon monoxide (SCO )inin POM reaction. CZ, (●) (●) selectivity of H2 ), (c) selectivity carbon monoxide ))CO in reaction. (■) (●) A3CZrZ, and A5CZrZ. Figure S6:The Mole fractions of carbon components selectivity ofofhydrogen hydrogen (S H2 ), (c) selectivity of carbon monoxide (S CO POM reaction. (■)(■) CZ, (●) CZ, (b) selectivity hydrogen (S ), (c) selectivity of carbon monoxide (S in POM reaction. (CZ, )(■) Supplementary Materials: following are available online at Figure www.mdpi.com/xxx/s1, Figure S1: Materials: The(e)following are online at(S www.mdpi.com/xxx/s1, S1: (S H2 CO selectivity ofavailable hydrogen (SH2 (c) selectivity of carbon monoxide (S ))POM in POM reaction. − 1−1 −1 −1 thanDeactivation CZ catalyst. Co-existence and does induce negative in the POM d condition: (■)rate CO, (●) CO2reaction: ,(▲) (▲) MeOHout, () balance. (a)°C CZ, CZrZ, A 11CZrZ, (▼) A (★) 555CZrZ, and CZ at 60 Gas Hourly Space Velocity in CZ, CZrZ, Au 5CZrZ, and (◊) CZ at 250 °C for 12 h in an neraging POM reaction: (■) CZ, CZrZ, Au 5(■) CZrZ, and (◊) Au 5(★) CZ at 250 for hA55Au ((●) )POM CZrZ, ((★) )of CZrZ, (AZrO A33Carbon (not )A CZrZ, and (12 )A CZ Kh Gas Hourly Velocity CZrZ, (▲) A CZrZ, (▼) 3CZrZ, CZrZ, (★) A and (◊) 5effect CZ5an at 60 Kh Gas Hourly Space Velocity CZrZ, (▲) A (▼) CZrZ, (★) A CZrZ, and (◊) A CZ at 60 Kh Gas Hourly Space Velocity 1CZrZ, 3)(●) 5A 5in 1Au CZrZ, (▲) A1CZrZ, (▼) A3CZrZ, (★) A5−1CZrZ, and (◊) A5CZ at 60 Kh−1 Gas Hourly Space Velocity −1 − −1 4fof −1 1(a) −1 −1 ure S7:However, XPS Au (BE in(GHSV) 82–97 ev) (Fresh): Abe 1CZrZ, (b) A 3Space and (c)(WHSV) accelerated aging condition (60 Kh of GHSV and 47.4 hCZrZ, ofthe WHSV). Figure S2: XRD profiles different ondition (60ofKh GHSV and 47.4 h9.48 of Figure S2: XRD profiles of different −1 tion. optimized conditions cannot reached with existence of only Au or ZrO.===of (GHSV) and 9.48 hh Weight Hourly Velocity (WHSV) with O 22/MeOH 0.5. and h WHSV). Weight Hourly Space Velocity with O /MeOH 0.5. (GHSV) and 9.48 Weight Hourly Space Velocity (WHSV) with /MeOH 2O (GHSV) and 9.48 h Weight Hourly Space Velocity (WHSV) with O =0.5. 0.5. 2/MeOH (GHSV) 9.48 h−1A Weight Hourly Space Velocity (WHSV) with 0.5. 2/MeOH dstate): to BEcatalysts in Au green lines are assigned to BE in Au )(e) and Figure S8: XPS(●) of (reduction state): (a) CZ, (b) CZrZ, (c)3+A 1CZrZ, (d) (◊) A 3CZrZ, and (e) Figure A5CZrZ. (◊) O Cu, (●) ZnO.=Figure (a) CZ,0;(b) CZrZ, (c)and A1CZrZ, (d) 3CZrZ, and A5CZrZ. Cu, ZnO. rZ, (b) S3: A3CZrZ, and (c) A5CZrZ, after 250 °C(b) for550 24 lines XRD profiles of CZrZ for catalysts calcination forh. 4(Blue hand at (a) 400 °C, °C, and (c) 750 °C. (◆) CuO, CZrZ catalysts after calcination 4 hPOM at after (a)at400 °C, °C, (c) 750are °C. (b) (◆)550 CuO, 3+) es are assigned to in 2Au (●) ZnO, (o)BE ZrO -tetragonal, (□)S4: ZrO 2-monoclinic. S4: Raman of (a) CZ, and (b) CZrZ. Table etragonal, (□) ZrO 2-monoclinic. Figure Raman spectra Figure of (a) CZ, and (b) spectra CZrZ. Table S1:surfaces Composition of catalyst measured byEDS EDSelement (%). Figure S5: The EDS element mapping profile: (a) catalyst measured by EDSsurfaces (%). Figure S5: The mapping profile: (a) coordinated the whole study and revised this manuscript. H.-Y.H. and H.-I.C. CZrZ, and (c) A(e) 1CZrZ, (d) A 3CZrZ, and (e) A 5CZrZ. Figure S6: components Mole fractions A1CZrZ,CZ, (d) (b) A3CZrZ, A5CZrZ. Figure S6: Mole fractions of carbon at of carbon components at xperiment. H.-Y.H. analyzed XRD, IR, XPS, and XANES data, and H.-I.C. 250 °C aging for 12condition: h in an accelerated aging (■) CO,() (●)Carbon CO2, (▲) MeOHout, () Carbon balance. (a) CZ, n accelerated (■) CO, (●) CO2condition: , (▲) MeOHout, balance. (a) CZ, properties of the catalysts and calculated the deactivation rates constant. CZrZ,S7: and (c)ofAAu 5CZrZ. Figure S7: ev) XPS(Fresh): of Au4f (a) (BEAin 82–97(b) ev)A(Fresh): (a) A(c) 1CZrZ, (b) A3CZrZ, and (c) A5CZrZ.(b) Figure XPS 4f (BE in 82–97 1CZrZ, 3CZrZ, and A5CZrZto(blue assigned to BE in Au0;togreen assigned in Au are assigned BE inlines Au0;are green lines are assigned BE inlines Au3+are ) and Figure to S8:BE XPS of 3+) and Figure S8: XPS of dv):no(a) external funding. Au 4f (BE in 82–97 ev):and (a) A 1CZrZ, (b) A 3CZrZ, and 5CZrZ, POMlines at 250 A 1CZrZ, (b) A3CZrZ, (c) A5CZrZ, after POM at (c) 250A°C for 24after h. (Blue are°C for 24 h. (Blue lines are assigned to assigned BE in Au0to ; green u0; green lines are BE inlines Au3+)are assigned to BE in Au3+) rs are grateful for the financial support of this work from the Ministry of RR PEER REVIEW of PEER REVIEW 16 of 19 19 wan. Author Contributions: Y.-J.H. coordinated thethis whole study andH.-Y.H. revisedand this16 manuscript. H.-Y.H. and H.-I.C. ons: Y.-J.H. coordinated the whole study and revised manuscript. H.-I.C. and processed the experiment. H.-Y.H. analyzed XRD, IR, and XPS,H.-I.C. and XANES data, and H.-I.C. essed prepared the experiment. H.-Y.H. analyzed XRD, IR, XPS, and XANES data, ors declare no conflict of only interest. The Au promoter the to CO but also The Au promoter not only enhanced the affinity affinity to adsorb adsorb CO but also increased measured thenot physicochemical of the catalysts and calculated the deactivation rates constant. sicochemical properties of theenhanced catalystsproperties and calculated the deactivation ratesincreased constant. to with CO the catalyst to react react withwrote CO on on the catalyst surface. surface. The The SSCO CO could could be be lowered lowered to to 6% 6% at at 200 200 H.-Y.H. this manuscript. manuscript.

ee features, features, the the A AxxCZrZ CZrZ catalyst catalyst produced produced aa good good catalytic catalytic performance, performance, reduced reduced

Funding: This research received no external funding. arch received no external funding. Figure of methanol as areaction. of Figure 2.2.Conversion Conversion ofto methanol as afunction function oftime-on-stream time-on-streamof ofPOM POMreaction reactionover over(■) (■)CZ CZ,, emperature, and maintained good durability in reaction. emperature, and still still maintained good durability in POM POM M.A.; Fierro, J.L.G. Partial oxidation of methanol produce hydrogen over −1 −1of Figure 1. Temperature profiles of catalyst performance: (a) conversion of methanol (C MeOH ), (b) Acknowledgments: The authors are grateful for the financial support of this work from the Ministry of : The authors are grateful for the financial support of this work from the Ministry of (●) CZrZ ,(★) A 5 CZrZ, and (◊) A 5 CZ at 250 °C for 12 h in an accelerated aging condition (60 Kh (●) CZrZ ,(★) A 5 CZrZ, and (◊) A 5 CZ at 250 °C for 12 h in an accelerated aging condition (60 Kh of pl. Catal. A Gen. 1997, 162, 281–297. Figure 2. Conversion of methanol as a function of time-on-stream of POM reaction over (■) CZ , −1 −1 Science and Technology of Taiwan. logy of Taiwan. selectivity of hydrogen (S H2 ), (c) selectivity of carbon monoxide (S CO ) in POM reaction. (■) CZ, (●) Figure 2. Conversion of methanol as a function of time-on-stream of POM reaction over (  ) CZ, aterials: The following are available online at www.mdpi.com/xxx/s1, Figure S1: Materials: The following are available online at www.mdpi.com/xxx/s1, Figure S1: GHSV and hh of GHSV and47.4 47.4 ofWHSV). WHSV). i, T. Selective production of hydrogen by partial oxidation of methanol over −1 ◦ − 1 −1 5 5 (●) CZrZ ,(★) A CZrZ, and (◊) A CZ at 250 °C for 12 h in an accelerated aging condition (60 Kh CZrZ, (▲) A1double CZrZ, (▼) A (★) 55CZrZ, and (◊) CZ at Gas Hourly Space POM reaction: (■) CZ, Au 55CZrZ, and (◊) at 250 °C in an n POM reaction: (■)Interest: CZ, Au CZrZ, and (◊) CZ atKh 250 °C for for 12 in an Velocity ((●) )3CZrZ, CZrZ, ((★) )A CZrZ, ( 159–167. ) AAu CZ at 60 250 C for 12 h12 inhhan accelerated aging condition (60 Kh of of 55Au ZnAl-layered hydroxides. Catal. Lett. 1999, 62, of The authors declare no conflict of55CZ interest. st: The Conflicts authors declare no(●) conflict of interest. −1 −1 −1 −1 −1 − 1WHSV). Figure 2.Although Conversion of methanol asS2: awere function of time-on-stream POM reaction overand (■) CZ , −1GHSV ondition (60 of and 47.4 h WHSV). Figure XRD profiles different ondition (60 Kh Kh of GHSV and 47.4 hthe of Figure S2: XRD profiles of different GHSV and 47.4 h of of WHSV). (GHSV) K.; and 9.48 hS.G.; Weight Hourly Space Velocity (WHSV) with Oby 2observed, /MeOH 0.5. above behaviors were observed, the interactions between Au the GHSV and 47.4 h of WHSV). Although the above behaviors the interactionsof between Au particles particles and the Jansson, Järås, Boutonnet, M. Production of hydrogen partial=of (a) (b) CZrZ, (c) 11CZrZ, (d) and (e) A CZrZ. (◊) Cu, (●) ZnO. Figure state): (a) CZ, CZ, (b)(●) CZrZ, (c) A A CZrZ, (d) A A33CZrZ, CZrZ, and (e) A55Appl. CZrZ. (◊) Cu, (●)12 ZnO. Figure 5CZ CZrZ ,(★) A5significantly CZrZ, andtechnique. (◊) A at 250 °C h and in an accelerated agingFor condition (60 Kh−1 of CZrZ might affect catalytic performance should be these CZrZ might significantly affect catalytic performance and should beexplored. explored. For thesepurposes, purposes, rstate): Cu/ZnO catalysts prepared by microemulsion Catal. Afor Gen. References CZrZ for 44−1 hhabove at 400 °C, °C, and (c) (◆) CuO, CZrZ catalysts catalysts after after calcination calcination for at (a) (a) 400 °C, (b) (b) 550 °C, and (c) 750 750 °C. °C. (◆) CuO, as the characteristics of A xbehaviors (x ==1, 3,3,5) catalysts are discussed Although the were the interactions between particles theand characteristics of A xCZrZ CZrZ (x550 1, 5)observed, catalysts are discussed asfollows. follows. GHSV 47.4 h of WHSV). Although the above behaviors were observed, the interactions between AuAu particles andand the the etragonal, ZrO -monoclinic. Figure S4: of and Table etragonal, (□) ZrO2Fierro, 2L.; -monoclinic. FigureM.A.; S4: Raman Raman spectra of (a) (a) CZ, and (b) (b) CZrZ. Table 1. (□) Alejo, Lago, R.; Peña, Fierro, J.L.G. Partial oxidation ofCZrZ. methanol o, R.; Peña, M.A.; J.L.G. Partial oxidation ofspectra methanol toCZ, produce hydrogen overto produce hydrogen over -T. Selective production of hydrogen from partial oxidation of methanol over CZrZ might significantly affect catalytic performance and should be explored. For these purposes, CZrZ might significantly affect catalytic performance and should be explored. For these purposes, the catalyst measured by (%). Figure The EDS element mapping catalyst surfaces surfaces measured by EDS EDS (%). FigureAS5: S5: The EDS element mapping profile: profile: (a) (a) CnZn-based catalysts. Appl. Catal. Gen. 1997, 162, 281–297. atalysts. Appl. Catal. A Gen. 1997, 162, 281–297. Table 1.1.The ignition temperature, Cu size, and deactivation rate Table The ignition temperature, Cu size, andas deactivation rateconstant. constant. peratures. Chem.the Commun. 2004, 1426–1427. characteristics of A CZrZ (x = 1, 3, 5) catalysts are discussed follows. x characteristics of A CZrZ (x = 1, 3, 5) catalysts are discussed as follows. x Although the above behaviors were observed, the interactions between Au particles and the 11CZrZ, (d) 33CZrZ, (e) A 55CZrZ. Figure S6: fractions of carbon at Aki, CZrZ, (d) A A CZrZ, and (e) A CZrZ. Figure S6: Mole Mole fractions of hydrogen carbon components at Velu, S.; and Suzuki, K.; Osaki, T.hydrogen Selective production of by partial oxidation of methanol over K.; 2. Osaki, T. Selective production of by partial oxidation of components methanol over n of methanol partial oxidation over supported platinum catalyst. Catal. Today nn accelerated aging condition: (■) (●) 22,, (▲) () Carbon balance. (a) accelerated agingmight condition: (■) CO, CO, (●) CO CO (▲) MeOHout, MeOHout, () Carbon balance. (a) CZ, CZ, Reduction State After POM Reaction Deactivation Rate Reduction State After POM Reaction d(Cu)be explored. Deactivation Rate purposes, CZrZ significantly catalytic performance should For these catalysts derived from CuZnAl-layered double hydroxides. Catal. Lett.and 1999, 62,d(Cu) 159–167. ved from CuZnAl-layered double hydroxides. Catal. Lett. 1999, 62, 159–167. Sample Ti Sample Ti affect aanm aasize, bb±CI cc(hr−1 55CZrZ. S7: XPS of Au 4f in 82–97 ev) (Fresh): (a) A 11CZrZ, (b) A 33CZrZ, and (c) Asselbo, CZrZ.3.Figure Figure S7: XPS of Au 4f (BE (BE in 82–97 ev) (Fresh): (a) A CZrZ, (b) A CZrZ, and (c) Table 1. The ignition temperature, Cu and deactivation rate constant. d(Cu) d(Cu) nm Increase % Constant d(Cu) nm d(Cu) nm Increase % Constant ± CI (hr−1)) Agrell, J.;K.;Hasselbo, K.; Jansson, K.;M.Järås, S.G.; Boutonnet, M. Production by partial K.;the Jansson, Järås, S.G.; Boutonnet, of hydrogen bydiscussed partial of hydrogen xCZrZ characteristics ofoxidation Aare =Production 1, 3, 5) catalysts are as follows. .are Hydrogen partial of (x methanol over copper-zinc 00;; green 3+ 3+) assigned to lines assigned to BE in Au and Figure S8: XPS of are assignedproduction to BE BE in in Au Auvia green lines are assigned to BE in Au ) and Figure S8: XPS of CZ 180 6.25 19.50 212 ±±0.0238 CZ prepared 180 6.25 prepared 19.50Catal. A Gen. 212 Appl. Catal.0.358 0.358 0.0238 oxidation methanol over Cu/ZnO catalysts by microemulsion technique. A Gen. methanol over Cu/ZnOof catalysts by microemulsion technique. Appl. ,v): 24,(a) 287–297. Reduction State Reaction Deactivation Rate v): A after at °C 24 lines (a) A11CZrZ, CZrZ, (b) (b) A A33CZrZ, CZrZ, and and (c) (c) A A55CZrZ, CZrZ, after POM POM at 250 250After °C for forPOM 24 h. h. (Blue (Blue lines are are d(Cu) CZrZ 175 5.40 12.24 127 0.202 ± 0.0248 2001, 211, 239–250. –250. CZrZ 175 5.40 12.24 127 0.202 ± 0.0248 Sample Ti 3+ 3+)) Active Cu/ZnO a nm temperature, a nm b ± CI c (hr−1) Y.; Morioka, H.; K.;to K. and Cu/ZnO/Al 2O 3size, and deactivation uu00;; green are assigned BE in green lines lines areTakaki, assigned toTakehira, BE in Au Au1. Table The ignition Cu rate constant. d(Cu) d(Cu) Increase % Constant 4. C.-T. Mo,Selective L.; Zheng, Yeh, C.-T. Selectivefrom production of hydrogen from partial oxidation over , X.; Yeh, production of120 hydrogen of methanol over A 3.97 9.00 127 0.191 ±±0.0253 A5X.; 5CZrZ CZrZ 120 3.97partial oxidation 9.00 127 of methanol 0.191 0.0253 ogeneous precipitation method in steam reforming of methanol. Appl. Catal. A CZ 6.25 19.50 212 0.358 ± 0.0238 ons: Y.-J.H. coordinated the whole study and revised this manuscript. and ons: Y.-J.H. coordinated theA whole study and1426–1427. revised this manuscript. H.-Y.H. and H.-I.C. H.-I.C. 257 silver catalysts at low temperatures. Chem. Commun. 2004, H.-Y.H. 1426–1427. s at low temperatures. Chem. 2004, 5Commun. 125 3.30 11.78 0.351 ±±0.0256 A 5CZ CZ180 125 3.30 11.78 257 0.351 0.0256 Reduction State After POM Reaction d(Cu) Deactivation Rate essed the H.-Y.H. analyzed IR, XPS, and XANES data, and H.-I.C. essedIgnition the experiment. experiment. H.-Y.H. analyzed XRD, IR, partial XPS,from and XANES data, and H.-I.C. 175 5.40 12.24 0.202 ± 0.0248 aa Normal bb Deactivation 5. Wan, A.; CZrZ Yeh, C.-T. Ignition of XRD, methanol oxidation over supported platinum127 catalyst. Catal. Today C.-T. of methanol partial oxidation over supported platinum catalyst. Catal. Today Sample Ti diameter estimated XRD using the Debye-Scherrer equation. Normal diameter estimated from XRD data data using the Debye-Scherrer equation. Deactivation Y.; Morioka, H.; Takehira, K. Production of hydrogen from methanol over a a b d(Cu) nm the d(Cu) nmconstant. % Constant ± CI c (hr−1) icochemical2007, properties of and rates sicochemical properties of the the catalysts catalysts and calculated calculated the deactivation deactivation rates constant. Increase cc95%9.00 129, –296. 5293–296. A CZrZ 120 3.97 127 0.191 ± 0.0253 rate constant calculated by Equation S1. Confidence interval (CI). rate constant calculated by Equation S1. 95% Confidence interval (CI). O3 catalysts prepared by homogeneous precipitation: Steam reforming and manuscript. manuscript. CZT.-J.;production 180S.-W. 6.25 19.50 212 0.358 ± 0.0238 Wang, production via partial oxidation of methanol over copper-zinc Wang, 6.S.-W.Huang, Hydrogen viaHydrogen partial oxidation of methanol over copper-zinc

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Table 1. The ignition temperature, Cu size, and deactivation rate constant. Sample

Ti

Reduction State d(Cu) a nm

After POM Reaction d(Cu) a nm

d(Cu) Increase %

Deactivation Rate Constant b ± CI c (hr−1 )

CZ CZrZ A5 CZrZ A5 CZ

180 175 120 125

6.25 5.40 3.97 3.30

19.50 12.24 9.00 11.78

212 127 127 257

0.358 ± 0.0238 0.202 ± 0.0248 0.191 ± 0.0253 0.351 ± 0.0256

a

Normal diameter estimated from XRD data using the Debye-Scherrer equation. calculated by Equation S1. c 95% Confidence interval (CI).

b

Deactivation rate constant

2.2. Physiochemical Properties of the CZ Catalysts with ZrO2 and Gold Promoter The physiochemical properties of catalysts are listed in Table 2. The metallic composition is similar to the stoichiometric calculation. The XRD patterns of fresh and reduced catalysts are shown in Figure 3c–g and Figure S2, respectively. ZrO2 diffraction peaks were not observed in all catalysts, which indicated that the ZrO2 might be the amorphous or poorer crystallization forms of ZrO2 . Figure S3 shows that the tetragonal structure (t-ZrO2 ) and tetragonal with monoclinic structure (m-ZrO2 ) were formed when the calcination temperature was above 550 ◦ C and 750 ◦ C, respectively. The Raman spectrum of CZrZ in Figure S4b shows that no band corresponding to t-ZrO2 and m-ZrO2 was detected, which also indicates that the ZrO2 was amorphous [32]. Moreover, the diffraction peak of Cu2 ZnZr (110) (JCPDS no. 65-6823) at 2θ of 42.14◦ was not observed. Thus, the ZrO2 was amorphous, and no mixed oxides (Cu, Zn, and Zr) were formed over CZrZ after 400 ◦ C calcination. The variation of surface area might vary with ZrO2 or/and gold promoters. Generally, the amorphous phase of zirconium exhibits a high surface area [12]. The surface area of CZ with Zr or Zr/Au increased from 34.59 to 77.52 m2 /g, and from 64.06 to 77.03 m2 /g, respectively. It seems that gold had minor effect on surface area. Table 2 also shows that the Cu dispersion was improved with incremental Au loading, e.g., the A5 CZrZ was 7% higher than the CZ and CZrZ catalysts. The sizes of CuO, Cu, and ZnO were estimated by CuO (111) XRD peak at 38.7◦ , Cu (200) XRD peak at 50.3◦ and ZnO (101) XRD peak at 36.2◦ , respectively, through the Debye-Scherer formula. The results show that CuO and Cu sizes decreased with the addition of ZrO2 (lowering from 5.65 nm to 4.49 nm and 6.25 nm to 5.4 nm, respectively) and also led to the formation of the smaller ZnO crystallite (from 9.03 nm to 6.42 nm). The weaker and broader copper diffraction peak of CuO (111) was observed from the CZrZ catalyst with the addition of gold. The CuO size decreased from 4.49 nm to 3.48 nm, and the size of Cu of reduced catalysts was down from 5.4 nm to 3.97 nm. The composition of catalysts surfaces calculated by XPS and Energy Dispersive Spectrometer (EDS) (Table 2 and Table S1) indicated a small amount of ZrO2 on the surface. In addition, the Au proportion was higher than the stoichiometric calculation, which indicated that most of the gold was on the catalyst surface. The EDS spectra are listed in Figure S5. Transmission electron microscope (TEM) images of Ax CZrZ catalysts shown in Figure 4a–c also show that gold particles were well-dispersed on catalysts with sizes around 2–5 nm. The mean sizes of Au of A1 CZrZ, A3 CZrZ, A5 CZrZ are 2.66 nm, 2.67 nm, and 3.09 nm, respectively. Generally, 3–10 nm-sized catalysts can perform higher activity due to more interface and higher surface area [33]. In addition, the solid black points are Au nanoparticles. The presence of Au (111) with 0.23 nm lattice fringes reportedly could exhibit high activity for oxidation reactions [34,35], and 0.25 nm corresponds to the wurtzite ZnO planes (101) of lattice fringes (shown in the high resolution TEM (HR-TEM) images in Figure 5a–c). Figure 5d shows the selected area electron diffraction (SAED) patterns of A5 CZrZ. Au (111), CuO (111), ZnO (100), ZnO (101), and ZnO (102) were detected, but no tetragonal ZrO2 (101) was observed, which indicated the existence of amorphous phase ZrO2 . This result corresponds to XRD profiles in Figure 3.

2ZnZr (110) (JCPDS no. 65-6823) at 2θ of 42.14o was not Moreover, the diffraction peak of Cuobserved. Thus, the ZrO2 was amorphous, and no mixed oxides (Cu, Zn, and Zr) were formed over observed. Thus, the ZrO2 was amorphous, and no mixed (Cu, Zn, andvariation Zr) wereof formed over CZrZ after 400 °Coxides calcination. The surface area might vary with ZrO2 or/and gold 2 or/and gold CZrZ after 400 °C calcination. The variation of surface area might vary with ZrO promoters. Generally, the amorphous phase of zirconium exhibits a high surface area [12]. The promoters. Generally, the amorphoussurface phase of zirconium exhibits high surface area [12]. Theto 77.52 m2/g, and from 64.06 to 77.03 area of CZ with Zr oraZr/Au increased from 34.59 2/g, and from 64.06 to 77.03 surface area of CZ with Zr or Zr/Au increased from 34.59 to 77.52 m 2 m /g, respectively. It seems that gold had minor effect on surface area. Table 2 also5shows Catalysts 2018, 8, 345 of 19 that the m2/g, respectively. It seems that gold had effectwas on surface area. Table 2 also shows that the e.g., the A5CZrZ was 7% higher than Cu minor dispersion improved with incremental Au loading, Cu dispersion was improved with incremental AuCZrZ loading, e.g., the A5CZrZ was 7% higher the CZ and catalysts. The sizes of CuO, Cu, andthan ZnO were estimated by CuO (111) XRD Physicochemical properties of the catalysts measured by various methods. the CZ andTable CZrZ2. catalysts. The sizes of CuO, Cu, and ZnO were estimated by CuO (111) XRD peak at 38.7°, Cu (200) XRD peak at 50.3° and ZnO (101) XRD peak at 36.2°, respectively, through peak at 38.7°, Cu (200) XRD peak at 50.3° and ZnO (101) XRD peak at 36.2°, respectively, through the Debye-Scherer formula. The results show that CuO and Cu sizes decreased with the addition Metallic Composition a BET dCuO dCu dZnO the Debye-Scherer formula. The results CuO and Cu sizes decreased with theofaddition Cu Composition Catalyst Surfaces d (%) cZrO2 that ofshow (lowering from (wt.%) Surface Area (nm) (nm) c (nm) c 5.65 nm to 4.49 nm and 6.25 nm to 5.4 nm, respectively) and also led to the Sample Dispersionfrom 5.65 nm to 4.49 nm and 6.25 nm to 5.4 nm, respectively) and also led to the of ZrO2 (lowering Name formation of the smaller ZnO crystallite (from 9.03 nm to 6.42 nm). Au0The /Au3+ weaker and broader (%) b 2 /g) Zn2p Cu2p Zr3d broader Au4f The weaker Cu (111) (from Cu (200) Zn to (101) Zrformation Zn Au Cu of the smaller(mZnO crystallite 9.03 nm 6.42 nm). and Fresh After with POM the addition of copper diffraction peak of CuO (111) was observed from the CZrZ catalyst copper diffraction peak of CuO (111) was observed from the CZrZ catalyst with the addition of CZ – 29.8 – 70.2 20.51 34.59 5.65 – – nm, and 73.76the size– of Cu of reduced – gold. The6.25 CuO size 9.03 decreased from 4.4926.24 nm to 3.48 catalysts was CZrZ – 31.2 15.9gold. 52.9The CuO 21.02 77.52 from 4.49 4.49nm to 3.48 5.40nm, and 6.42 –Cu of reduced 27.85 3.38 68.77 – size decreased the catalysts was down from 5.4 nm to 3.97size nm.ofThe composition of catalysts surfaces– calculated by XPS and Energy A1 CZrZ 1.0 31.4 15.4 52.2 26.93 4.81 4.33 27.45 4.39 58.09 0.65 0.83 down from 5.4 nm to 3.9764.06 nm. The composition of catalysts6.96 surfaces 10.07 calculated XPS and Energy Dispersive Spectrometer (Tables28.29 2by and S1)4.89 indicated a small0.85 amount of ZrO2 on the surface. A3 CZrZ 3.1 31.6 15.6 49.7 28.32 73.21 4.09 4.28 5.98 (EDS) 10.18 56.64 1.11 Spectrometer (EDS) 2 and S1)3.97 indicated aproportion small amount ZrO2 than on 3.72 thethe surface. A5 CZrZ 4.5 31.7 16.7Dispersive 47.1 27.92 77.03 (Tables 3.48 11.59was of 26.35 58.34 1.37 calculation, 1.43 which indicated In addition, the Au5.69 higher stoichiometric a Calculated Metallic Composition c Normal diameter In addition, the coupled Au proportion was higher than calculation, which indicated by inductively plasma mass spectrometry (ICP-MS). Calculated Cu the dispersion of catalysts byThe N chemisorptions. that most ofthe thebstoichiometric gold was on catalyst surface. spectra are listed in Figure S5. 2 OEDS d estimated from XRD data usingthat the Debye-Scherrer equation. Calculated from XPS. most of the gold was on the catalyst surface. The EDS spectra are listed in Figure S5.

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of active oxygen. The Au promoter not only enhanced the affinity to adsorb CO but also increased moveable oxygen to react with CO on the catalyst surface. The SCO could be lowered to 6% at 200 °C. Based on these features, the AxCZrZ catalyst produced a good catalytic performance, reduced Sco and ignition temperature, and still maintained good durability in POM reaction. Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Figure S1: Deactivation rate in POM reaction: (■) CZ, (●) CZrZ, (★) Au5CZrZ, and (◊) Au5CZ at 250 °C for 12 h in an −1 of XRD profiles of fresh CuO,S2:(b)XRD ZnO, (c) CZ, CZrZ, (e) A1CZrZ, (f) accelerated aging conditionFigure (60 Kh3. GHSV and 47.4 h−1 ofcatalysts: WHSV). (a) Figure profiles of (d) different Figure 3. XRD profiles of fresh (a) CuO, (b) (e) ZnO, (c) CZ, (d) CZrZ, (e) A1(e) CZrZ, (f) (◆(◊) A 3CZ, CZrZ, and (g) A5CZrZ. (5CZrZ. CuO ZnO. catalysts state): (b) CZrZ, (c) 1CZrZ, 3CZrZ, and Cu,)(●) Figure (●) Figure 3. XRD profiles of fresh catalysts: (a)(reduction CuO, (b) catalysts: ZnO, (c)(a) CZ, (d) CZrZ, A1A CZrZ, (f)(d) A3A CZrZ, and (g) A5A CZrZ. ) CuO ( ) ZnO. A3CZrZ, andXRD profiles (g) A5CZrZ. ( ◆ ) for 4 h CuO ZnO. S3: of CZrZ catalysts after calcination at (a) 400 (●) °C, (b) 550 °C, and (c) 750 °C. (◆) CuO, (●) ZnO, (o) ZrO2-tetragonal, (□) ZrO2-monoclinic. Figure S4: Raman spectra of (a) CZ, and (b) CZrZ. Table S1: Composition of catalyst surfaces measured by EDS (%). Figure S5: The EDS element mapping profile: (a) CZ, (b) CZrZ, (c) A1CZrZ, (d) A3CZrZ, and (e) A5CZrZ. Figure S6: Mole fractions of carbon components at 250 °C for 12 h in an accelerated aging condition: (■) CO, (●) CO2, (▲) MeOHout, () Carbon balance. (a) CZ, (b) CZrZ, and (c) A5CZrZ. Figure S7: XPS of Au4f (BE in 82–97 ev) (Fresh): (a) A1CZrZ, (b) A3CZrZ, and (c) A5CZrZ (blue lines are assigned to BE in Au0; green lines are assigned to BE in Au3+) and Figure S8: XPS of Au4f (BE in 82–97 ev): (a) A1CZrZ, (b) A3CZrZ, and (c) A5CZrZ, after POM at 250 °C for 24 h. (Blue lines are assigned to BE in Au0; green lines are assigned to BE in Au3+)

surface area [33]. In addition, the solid black points are Au nanoparticles. The presence of Au (111) with 0.23 nm lattice fringes reportedly could exhibit high activity for oxidation reactions [34,35], and 0.25 nm corresponds to the wurtzite ZnO planes (101) of lattice fringes (shown in the high resolution TEM (HR-TEM) images in Figure 5a–c). Figure 5d shows the selected area electron diffraction (SAED) patterns of A5CZrZ. Au (111), CuO (111), ZnO (100), ZnO (101), and Catalysts 2018, 8, 345 6 of 19 ZnO (102) were detected, but no tetragonal ZrO2 (101) was observed, which indicated the existence of amorphous phase ZrO2. This result corresponds to XRD profiles in Figure 3.

(a)

20 nm 20 nm

(b)

10 nm 10 nm

(c)

10 nm 10 nm

Figure 4. TEM images andand mean sizesize of (a) (b) A andand (c) A Figure 4. TEM images mean ofA (a) A1CZrZ, (b) A3CZrZ, (c)5 CZrZ. A5CZrZ. 1 CZrZ, 3 CZrZ,

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Figure 5. 5. HR-TEM images of of (a)(a) A1A CZrZ, (b)(b) A3CZrZ, (c) (c) A5CZrZ, andand (d) (d) SAED of A Figure HR-TEM images A3 CZrZ, A5 CZrZ, SAED of5CZrZ. A5 CZrZ. 1 CZrZ,

InInsummary, be improved improved by by the summary,the thesize, size,Cu Cudispersion, dispersion,and andsurface surfacearea area of of the the fresh fresh CZ CZ could could be the addition of Zr or Au/Zr promoters. Copper with small particle size and high dispersion could addition of Zr or Au/Zr promoters. Copper with small particle size and high dispersion could improve improve methanol conversion [36,37]. However, is very important evaluate whether thosecan methanol conversion [36,37]. However, it is very it important to evaluatetowhether those properties properties can be maintained after The POM reaction. XRD profiles of catalysts after reduction be maintained after POM reaction. XRD profilesThe of catalysts after reduction pretreatment and after pretreatment and after the POM reaction were utilized to estimate the variation of Cu size. The 1, the POM reaction were utilized to estimate the variation of Cu size. The results, shown in Table results, shown in Table 1, were calculated based on a Cu (200) peak at 50.3° through Debye-Scherer were calculated based on a Cu (200) peak at 50.3◦ through Debye-Scherer formula. As a matter of formula. matter of fact, the CZ andparticle A5CZ dimension catalysts show particletodimension to on fact, theAs CZa and A5 CZ catalysts show increasing more thanincreasing 200%, while more than 200%, while on CZrZ and A 5CZrZ samples, the corresponding value is about 120%. CZrZ and A5 CZrZ samples, the corresponding value is about 120%. After POM reaction, the XRD After POM reaction, XRD results that the catalyst with results indicate that the the catalyst with indicate zirconium would maintain highzirconium durabilitywould due tomaintain amorphous high durability due to amorphous ZrO functioning as textural promoter, which limited the ZrO functioning as textural promoter, which limited the growth of copper, stabilized the structure, growth of copper, stabilized the structure, and hampered the aggregation of Cu particles [38]. and hampered the aggregation of Cu particles [38]. Coke formation during the reaction might also be Coke formation duringtothe might also be a Low factor contributing thedue loss a factor contributing thereaction loss of catalytic activity. carbon balance to was to of thecatalytic possibility activity. Low carbon balance was due to the possibility that carbon was deposited on the catalyst that carbon was deposited on the catalyst [30]. The carbon balance of CZ, CZrZ, and A5 CZrZ in an 5CZrZ in an accelerated aging condition for 12 h [30]. The carbon balance of CZ, CZrZ, and A accelerated aging condition for 12 h (Figure S6) was close to 100%, so the coke was not the main factor (Figure was close of to catalysts. 100%, so the coke was not the main factor on the deactivation of catalysts. on theS6) deactivation 2.3. 2.3.Reducibility ReducibilityofofCatalyst Catalyst The can be bechanged changedbybyadding adding different promoters, which might Thereducibility reducibilityof of catalyst catalyst can different promoters, which might induce induce various catalytic performances. Temperature-programmed reduction (TPR) was used to various catalytic performances. Temperature-programmed reduction (TPR) was used to evaluate evaluate the reducibility of CZ could be improved by adding andpromoters. Au promoters. whetherwhether the reducibility of CZ could be improved by adding ZrO2ZrO and2 Au For For all the 2 allcatalysts, the catalysts, the H /Cu ratio is ca. 1.0 (1.02–1.00), which indicates full reduction of CuO to Cu the H2 /Cu ratio is ca. 1.0 (1.02–1.00), which indicates full reduction of CuO to Cu0 0[39]. [39]. Figure the profile TPR profile of which CuO, which board reduction at ◦200–250 Figure 6a is6a theisTPR of CuO, shows shows a boarda reduction profile atprofile 200–250 C, with a°C, main ◦ C. Sloczynski with a mainpeak reduction peak α233 at around 233 °C.etSloczynski etVelu al. [40] and Velu et al. [41] indicated reduction α at around al. [40] and et al. [41] indicated α peak might be + or crystallized copper oxide to metallic Cu. The α formed peak might from of Cucopper frombe theformed reduction of the Cu+reduction or crystallized oxide to metallic Cu. The reduction profile of reduction profile of CZ, 6b, shifts towith a lower temperature with α peak at 205 β°C CZ, shown in Figure 6b, shown shifts toina Figure lower temperature α peak at 205 ◦ C and a front shoulder peak ◦ and a front shoulder β peak at 188 °C. Fierro et al. [42] hypothesized that the β peak resulted when at 188 C. Fierro et al. [42] hypothesized that the β peak resulted when the well-dispersed copper came the well-dispersed copper camewhich into contact ZnO particle, which lowered the reduction into contact with ZnO particle, loweredwith the reduction temperature. The improved reducibility temperature. The improved reducibility of CuO was contributed to ZnO, which enhanced the spillover of hydrogen atoms [43,44]. The addition of zirconium had significant effect on the peaks

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of CuO was contributed to ZnO, which enhanced the spillover of hydrogen atoms [43,44]. The addition Catalysts 2018, 8, x FOR PEER REVIEW 9 of 19 of zirconium had significant effect on the peaks of α (at 190 ◦ C) and β (at 174 ◦ C). Wang et al. [45] indicated smaller copper particles canetexist on indicated catalyststhat with Zr prompter, and Tada al. [46] of αthat (at 190 °C) and β (at 174 °C). Wang al. [45] smaller copper particles can et exist illustrated that highly Cu in with amorphous improved catalytic activity. on catalysts withdispersed Zr prompter, andclose Tadacontact et al. [46] illustrated that ZrO highly dispersed Cu in close 2 2 improved with amorphous ZrOprofiles catalytic activity. Figure 6d–f shows the reduction profiles Figure contact 6d–f shows the reduction of catalysts containing gold that shifted to lower temperature. ◦ ◦ of catalysts containing gold that shifted to lower temperature. As the gold content increases from 1 As the gold content increases from 1 to 5%, the β peak shifts from 172 C to 158 C and the concomitant ◦ ◦ to 5%, the β peak shifts from 172 °C to 158 °C and the concomitant α peak shifts from 186 °C to had, 170 the α peak shifts from 186 C to 170 C. This obviously shows that the more gold content it °C. This obviously shows that the more gold content it had, the greater shifting effect could be greater shifting effect could be observed. Some research has indicated that gold particles could adsorb observed. Some research has indicated that gold particles could adsorb and then dissociate and then dissociate hydrogen [47]; hence, increasing gold content might enhance H2 adsorption and hydrogen [47]; hence, increasing gold content might enhance H2 adsorption and dissociation at dissociation at lower temperature. Dissociated hydrogen spilled over to neighboring copper oxide and lower temperature. Dissociated hydrogen spilled over to neighboring copper oxide and led to a led to alower lowerreduction reduction temperature. Moreover, the fraction of β peak to α peak temperature. Moreover, the fraction ratiosratios of β peak to α peak (Table(Table 3) on3) on Ax CZrZ are lower than CZrZ and CZ, which may be due to a smaller amount of ZnO on the surface. AxCZrZ are lower than CZrZ and CZ, which may be due to a smaller amount of ZnO on the In summary, the TPR data show that the catalysts with Zr/Au promoter really present a better surface. In summary, the TPR data show that the catalysts with Zr/Au promoter really present aredox which might provide a lower ignition temperature andconversion. better methanol ability, better whichredox mightability, provide a lower ignition temperature and better methanol conversion.

Table 3. Fractions of TPR area. Table 3. Fractions of TPR area.

Catalyst CZ CZrZ A1CZrZ A1 CZrZ A3 CZrZ A5 CZrZ Catalyst CZ CZrZ A3CZrZ A5CZrZ of β 5656 61 50 50 51 51 48 β 61 48 Fractions ofFractions TPR α 39 53 Area (%) TPR Area (%) α 4444 39 50 50 49 49 53

6. Hydrogen temperatureprogrammed programmed reduction profiles: (a) CuO, (b) CZ,(b) (c) CZ, CZrZ, Figure Figure 6. Hydrogen temperature reduction profiles: (a) CuO, (c)(d)CZrZ, A CZrZ, (e) A CZrZ, and (f) A CZrZ. 1 3 5 (d) A1 CZrZ, (e) A3 CZrZ, and (f) A5 CZrZ.

2.4. Oxygen Mobility of Catalyst

2.4. Oxygen Mobility of Catalyst

From the physiochemical properties and TPR data, we know that the particle size, Cu

From the physiochemical properties andof TPR we know that the particle size, Cu dispersion, 2 and Au promoters. dispersion, surface area, and reducibility CZ data, have been improved by ZrO surfaceHowever, area, and of see CZwhat haveproperties been improved by ZrO andthe AuSCO promoters. However, it it reducibility is interesting to induce lower SCO2. For , the CZrZ catalysts is interesting to see what properties induce lower S . For the S , the CZrZ catalysts showed showed the highest CO selectivity compared with CO other catalysts.CO The AxCZrZ catalysts were able the lower the SCO tocompared less than 10% 200 °C, the effectThe of which was catalysts proportional to able gold to content. highesttoCO selectivity withatother catalysts. Ax CZrZ were lower the prompter, has◦been improve oxygen mobility [23]. We assume thatprompter, oxygen as SCO to Gold less than 10% atas200 C, thereported, effect ofcan which was proportional to gold content. Gold CO decrement. mobility might be improve the reasonoxygen for the Smobility has been reported, can [23]. We assume that oxygen mobility might be the reason for the SCO decrement.

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We We used used X-ray X-ray photoelectron photoelectron spectroscopy spectroscopy (XPS), (XPS), temperature temperature program program desorption desorption of of oxygen oxygen We used X-ray photoelectron spectroscopy (XPS), temperature program desorption oxygen (O and X-ray absorption near-edge structure (XANES) to confirm oxygen mobility. Figure 77 2-TPD), (O2-TPD), and X-ray absorption near-edge structure (XANES) to confirm oxygen mobility.of Figure (O -TPD), and X-ray absorption near-edge structure (XANES) to confirm oxygen mobility. Figure shows the 2 shows the XPS XPS spectra spectra of of O1s O1s for for fresh fresh CZ, CZ, CZrZ, CZrZ, and and A A55CZrZ CZrZ catalysts catalysts fitted fitted to to two two peaks peaks (OI (OI and and7 shows the higher XPS spectra ofpeak O1s for fresh CZ,binding CZrZ, and A5 CZrZ catalysts two peakspresent (OI and OII). energy (OII) (with energy within 531–532 eV) OII). The The higher energy peak (OII) (with binding energy within 531–532fitted eV) is istocommonly commonly present OII). The higher energy peak (OII) (with binding energy within 531–532 eV) is commonly as non-lattice oxygen [48,49]. The order of area ratio of OII/OI is A > CZ (2.22) > CZrZ 5CZrZ (4.85) as non-lattice oxygen [48,49]. The order of area ratio of OII/OI is A5CZrZ (4.85) > CZ (2.22) >present CZrZ as non-lattice oxygen [48,49]. The order of area ratio of OII/OI is A CZrZ (4.85) > CZ (2.22) > CZrZ (1.42). The amorphous structure of Zr in CZ catalyst may be the main factor for the decrement of 5 (1.42). The amorphous structure of Zr in CZ catalyst may be the main factor for the decrement of (1.42). The amorphous structure of Zr in CZ catalyst may be the main factor for the decrement of OII. OII. Conversely, CZrZ with Au prompter could overcome this issue, and the A obviously 5CZrZ OII. Conversely, CZrZ with Au prompter could overcome this issue, and the A5CZrZ obviously Conversely, CZrZ with Auof prompter could overcome this issue, and the A obviously increased proportion OII peak. Furthermore, the was utilized to oxygen 5 CZrZ increased the the proportion of OII in in O1s O1s peak. Furthermore, the O O22-TPD -TPD was utilized to test testincreased oxygen the proportion of OII in O1s peak. Furthermore, the O -TPD was utilized to test oxygen chemisorption chemisorption ability. Figure 8 shows the O profiles of CZ, CZrZ, and A 2-TPD 5CZrZ catalysts. 2 chemisorption ability. Figure 8 shows the O2-TPD profiles of CZ, CZrZ, and A5CZrZ catalysts. The The ability. Figure 8 desorption shows the peaks O profiles of CZ, CZrZ, A5 CZrZ catalysts. The CZaacatalyst CZ had at °C 400–450 °C. CZrZ minor 2 -TPD CZ catalyst catalyst had desorption peaks at around around 225–300 225–300 °C and andand 400–450 °C. The The CZrZ showed showed minor ◦ C and 400–450 ◦ C. The CZrZ showed a minor peak at had desorption atlarge around 225–300 peak at °C peak at °C. peak at 250–300 250–300peaks °C and and large peak at 350–450 350–450 °C. The The A A55CZrZ CZrZ catalyst catalyst started started to to desorb desorb oxygen oxygen at at ◦ C and large peak at 350–450 ◦ C. The A CZrZ catalyst started to desorb oxygen at 125 ◦ C and 250–300 125 °C and apparently had an oxygen consumption peak at 200–450 °C. Clearly, the oxygen 5 125 °C and apparently had an oxygen consumption peak at 200–450 °C. Clearly, the oxygen ◦ apparently an oxygen consumption at 200–450 Clearly, the oxygen mobility is related mobility related to in When higher OII/OI is aa lower oxygen mobility is ishad related to the the ratio ratio of of OII/OI OII/OIpeak in XPS. XPS. When aaC. higher OII/OI is present, present, lower oxygento − the ratio of OII/OI in XPS. When a higher OII/OI is present, a lower oxygen desorption temperature desorption desorption temperature temperature is is found. found. Non-lattice Non-lattice oxygen oxygen might might tend tend to to form form superoxide superoxide (O (O22−),), which whichis − found. oxygen might reaction tend to form superoxide (O2 ),the which would enhanceadsorption CO oxidation would enhance oxidation [50,51]. In order of is wouldNon-lattice enhance CO CO oxidation reaction [50,51]. In addition, addition, the order of oxygen oxygen adsorption is reaction In addition, the order of oxygen adsorption is A CZrZ > CZrZ > CZ. However, there 5CZrZ[50,51]. A > CZrZ > CZ. However, there are more adsorbed oxygen molecules on the CZrZ than on 5 A5CZrZ > CZrZ > CZ. However, there are more adsorbed oxygen molecules on the CZrZ than on are adsorbed oxygen molecules on the CZrZ thanlimit on the CZ, and a higher desorption temperature the CZ, aa higher desorption temperature might the mobility of and in themore CZ, and and higher desorption temperature might limit the mobility of oxygen oxygen and result result in high high might limit the mobility of oxygen and result in high Sco on CZrZ. Sco on CZrZ. Sco on CZrZ.

Figure CZrZ. Figure 7. 7. XPS XPS spectra spectra of of O1s: O1s: (a) (a) CZ, CZ, (b) (b) CZrZ, CZrZ, and and (c) (c) A A555CZrZ. CZrZ.

Figure 8. of catalysts: Figure 8. 8. The The O O222-TPD -TPD of reduced reduced catalysts: (a) (a) CZ, CZ, (b) (b) CZrZ, CZrZ, and and (c) (c) A A555CZrZ. CZrZ. Figure The O -TPD of reduced catalysts: (a) CZ, (b) CZrZ, and (c) A CZrZ.

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Furthermore, to to better better realize a change in in reducibility andand Furthermore, realize the the properties propertiesofofgold goldfor forinducing inducing a change reducibility oxygenmobility, mobility, the the electron electron states and after POM 5CZrZ ininoxygen states of of gold goldand andcopper copperspecies specieson onfresh freshAA 5 CZrZ and after POM 4f x reaction were measured by XPS and XAS. The XPS Au profiles of A CZrZ catalysts fresh and reaction were measured by XPS and XAS. The XPS Au4f profiles of Ax CZrZ catalysts inin fresh and after after POM reaction are shown in Figures S7 and S8, respectively. All catalysts exhibit peaks POM reaction are shown in Figures S7 and S8, respectively. All catalysts exhibit peaks assigned as 0 and Au3+, and the 0ratio 3+ 0/Au3+ is listed in Table 2. 0/Au3+ ratio increases 0 and Au assigned as3+ Au Aulisted The 3+ Auratio Au , and the ratio of Au /Au of is in Table 2. The Au0 /Au increases as the Au as the Au loading amount increases (0.65–1.37). The metallic gold worked as the activeAu sitedeposited when loading amount increases (0.65–1.37). The metallic gold worked as the active site when Au deposited on irreducible oxide, such as Silica or ZnO (in this study), which indicated a weaker on irreducible oxide, such as Silica or ZnO (in this study), which indicated a weaker metal-support metal-support interaction between Au[52]. and Thus, support [52]. Thus, a higher of Au0induce ions might 0 ions might interaction between Au and support a higher portion of Auportion higher induce higher catalytic activity [53–55]. Moreover, higher electrical capacity and lower Fermi catalytic activity [53–55]. Moreover, higher electrical capacity and lower Fermi level of gold canlevel induce of gold can induce more electrons to go through the copper and transferring to Au [56], which may more electrons to go through the copper and transferring to Au [56], which may result in a smaller result in a smaller amount of Cu0 on A5CZrZ. The XPS results (Figure S8, Table 2) also show that amount of Cu0 on A5 CZrZ. The XPS results (Figure S8, Table 2) also show that the Au0 /Au3+ ratio of 0 3+ the Au /Au ratio of A5CZrZ after POM reaction (1.43) is higher than fresh (1.37). For copper A5 CZrZ after POM reaction (1.43) is higher than fresh (1.37). For copper species, XANES in Figure 9a,d species, XANES in Figure 9a,d shows that the fresh CZ and A5CZrZ catalysts consisted of 100% shows that the fresh CZ and A5 CZrZ catalysts consisted of 100% Cu2+ , a state that is non-active toward Cu2+, a state that is non-active toward reforming [1]. 0All catalysts were pre-reduced to Cu0 before reforming [1]. All catalysts were pre-reduced to Cu before POM reaction. Due to higher oxygen POM reaction. Due to higher oxygen mobility, gold deposited on CZrZ catalyst can adsorb/desorb mobility, gold deposited on CZrZ catalyst can adsorb/desorb more oxygen atoms and spill them more oxygen atoms and spill them over to copper and keep more partially reduced copper [23], over to copper and keep more partially reduced copper [23], which results in the more active species which results in the more active species Cu+ on the catalytic surface after POM reaction. Figure Cu+ on the catalytic surface after POM reaction. Figure 9b,e indicates that the A5 CZrZ had a higher 9b,e indicates that the A5CZrZ had a higher percentage of Cu2O (47.3%)0 compared with CZ (39.4%) percentage of Cu2 O (47.3%) compared with CZ (39.4%) and less Cu (A5 CZrZ 52.73%, CZ 60.6%). and less Cu0 (A5CZrZ 52.73%, CZ 60.6%). Oguchi et al. [57] indicate that Cu2O was the major active Oguchi et al. [57] indicate that Cu2 O was the major active site for methanol reforming as a result of site for methanol reforming as a result of higher oxidation and reduction ability. However, after an higher oxidation and reduction ability. However, after an extended duration test (over four months) extended duration test (over four months) (Figure 9c,f), a large volume of oxygen diffused into (Figure 9c,f), a large volume of oxygen diffused into2+the lattice of copper species, and the content of the2+lattice of copper species, and the content of Cu increased to 53.6%, higher than the sum of + and Cu0 on CZ. While less Cu2+ (37.8%) formed, Cu to 53.6%, higher than sum of Cu 2+ (37.8%) Cu+ increased and Cu0 on CZ. While less Cuthe formed, Cu0 and Cu+ were the main species on 0 and Cu+ were the main species on A CZrZ. This indicates that the Au promoter enhanced the Cu 5 A5CZrZ. This indicates that the Au promoter enhanced the mobility of oxygen and reduced the mobility of oxygen and reduced the accumulation oxygen on theXPS, copper-active site.XANES As the result, accumulation of oxygen on the copper-active site.ofAs the result, O2-TPD, and all XPS, O -TPD, and XANES all indicated that the Au promoter could enhance the oxygen mobility. 2 indicated that the Au promoter could enhance the oxygen mobility.

◦ Figure ofof CuCu species onon (a)(a) fresh CZ,CZ, (b) (b) CZ CZ during POM at 250 Figure9.9.The Thecompound compoundfitfitXANES XANESspectra spectra species fresh during POM at C ◦ for (c)24 CZh,after POM 4 over months, (d) fresh (e) A5(e) CZrZ during POM at 250 C for 25024°Ch,for (c) CZ afterover POM 4 months, (d)A fresh A5CZrZ, A5CZrZ during POM at 250 5 CZrZ, 24 h, and (f) A CZrZ after POM over 4 months. °C for 24 h, and 5 (f) A5CZrZ after POM over 4 months.

2.5. In-Situ DRIFTS

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2.5. In-Situ DRIFTS To better understand how the Au promoter affects the intermediates during the POM reaction, in-situ DRIFTS how was the usedAu topromoter examine affects the POM mechanism. Figure presents the To better understand the intermediates during10a–f the POM reaction, FT-IR DRIFTS spectra of A5CZrZ catalyst under reaction temperatures 100 °C, 125 °C, 175 °C, 200 °C, in-situ was used to examine thethe POM mechanism. Figureof 10a–f presents the FT-IR spectra ◦ ◦ ◦ ◦ ◦ −1 250 °C, and 300 °C. At 100 °C, the C–H stretching peaks at 2930 and 2819 cm . Also C–O stretching of A5 CZrZ catalyst under the reaction temperatures of 100 C, 125 C, 175 C, 200 C, 250 C, and ◦ C. At 1 . Also −1 stretching peaks at 1446, 1076 of methoxy group [58] and was2819 found, 1153C–O cm−1 was assigned as 1446, the 300 100 ◦ C, the cm C–H peaks at 2930 cm−and stretching peaks at − 1 − 1 on-top C–O stretching onwas Zr4+found, [59]. The electron affinity ofassigned Au enhanced adsorption of 1076 cmmethoxy of methoxy group [58] and 1153 cm was as thethe on-top methoxy 4+ CH3OH, and methoxy species onaffinity the surface the catalyst. Hydrogen from C–O stretching on Zr [59]. Theformed electron of Auofenhanced the adsorption of CHmethanol 3 OH, and reacted with oxygen, thus forming theofhydroxy group, which showed a broadreacted band atwith 3100–3500 methoxy species formed on the surface the catalyst. Hydrogen from methanol oxygen, cm−1forming . The peaks at 1592 and 1367which cm−1 were assigned asband mono-dentate formate asymmetric thus the hydroxy group, showed a broad at 3100–3500 cm−1(OCO . The peaks at 1592 − 1 and1367 symmetric stretching), which was formed from(OCO the methoxy group interacting stretching), with the and cm were assigned as mono-dentate formate asymmetric and symmetric oxygen atom adsorbed ontomethoxy the catalyst surface [58]. After temperatures higher than ignition which was formed from the group interacting with the oxygen atom adsorbed onto the ◦ temperature (>120 °C), the DRIFTS spectra were obviously different in the region of C–H catalyst surface [58]. After temperatures higher than ignition temperature (>120 C), the DRIFTS − 1 −1 stretching ). Theinbi-dentate which peaks at 2964, cm 2865,). and cm−1 spectra were(3000–2700 obviously cm different the regionformate, of C–H stretching (3000–2700 The 2739 bi-dentate − 1 ◦ [58,60,61], formed at 125 °C. The formate is ancm intermediate the formation and CO 2, CO 2. formate, which peaks at 2964, 2865, and 2739 [58,60,61],informed at 125 of C. H The formate is an The bidentate was reported toand decompose COO* (*:formate metal site), H*, or CO* and OH*, intermediate in formate the formation of H2 , CO CO2 . Thetobidentate was reported to decompose ◦ C, the 2 and produced CO CO At 175 °C,and theproduced bi-dentateCO formate decomposed very quickly, and toand COO* (*: metal site), H*, or [61]. CO* and OH*, and CO [61]. At 175 bi-dentate 2 minor decomposed peaks were very observed. Furthermore, the methoxy and mono-dentate formate peaks formate quickly, and minor peaks were observed. Furthermore, the methoxy and decreased andformate almost peaks disappeared at temperatures higher thanat 200 °C. At 300 °C, onlythan carbonate mono-dentate decreased and almost disappeared temperatures higher 200 ◦ C. ◦ species (CO CO2(g), andspecies H2O(g),(CO were 3*), carbonate At 300 C, only CO2(g) , and H2 O(g) , were observed. 3 *),observed.

◦ C,175 ◦ C, Figure10. 10. DRIFT spectra reaction at at (a)(a) 100100 °C,◦(b) 125 125 °C, (c) Figure spectra of ofAA5CZrZ duringPOM POM reaction C, (b) (c) °C, 175(d) 5 CZrZduring ◦ ◦ ◦ 200 °C, C, (e)(e) 250250 °C, C, and (f) (f) 300300 °C. C. (d) 200 and

Figure11 11(I) (I)a–c a–cshows showsthe theDRIFTS DRIFTSspectra spectrafrom from3400–2600 3400–2600 cm cm−−11 of Figure of CZ, CZ, CZrZ, CZrZ, and and A A55CZrZ CZrZ catalysts during POM reaction at 125 °C. Methoxy group was observed on the surface of CZ ◦ catalysts during POM reaction at 125 C. Methoxy group was observed on the surface of CZand and CZrZ,but butonly only formate group be detected on A5Literature CZrZ. Literature [58,62] CZrZ, thethe formate andand –OH–OH group couldcould be detected on A5 CZrZ. [58,62] indicates indicates thatdehydrogenated methanol dehydrogenated to afterwards CH3O, then afterwards dehydrogenated to CH2O that methanol to CH3 O, then dehydrogenated to CH2 O (formaldehyde) in the POM reaction mechanism. The CH2O preferred to react with oxygen to in(formaldehyde) the POM reaction mechanism. The CH 2 O preferred to react with oxygen to form CH2 OO and 2OO and dehydrogenate to formate (HCOO). However, the rapid oxidation of form CH dehydrogenate to formate (HCOO). However, the rapid oxidation of formaldehyde led to difficulty to difficulty peaks in detecting formaldehyde peaksKulkarni in the DRIFTS spectra [61]. informaldehyde detecting theled formaldehyde in the the DRIFTS spectra [61]. et al. [63] indicated 3OH favored dehydrogenation Kulkarni et favored al. [63] indicated that CHto to methoxy on the Cu0 that CH3 OH dehydrogenation methoxy on the Cu0 surface, and the Cu+ -rich surface surface, and the Cu+-rich surface tended toward oxidization of the methoxy species to formate. The A5CZrZ with higher Cu+/Cu0 ratio and better oxygen mobility could speed up the formation

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+ 0 tended toward of the methoxy species to formate. The A5 CZrZ with higher13Cu Catalysts 2018, 8, xoxidization FOR PEER REVIEW of 19/Cu ratio and better oxygen mobility could speed up the formation of formate at lower temperatures. of formate formate at lower temperatures. The formate transferred to H2, H2O, CO2, and CO very quickly, The transferred to H2 , H2 O, CO 2 , and CO very quickly, while the adsorbed formate peaks ◦ C.AObviously, while the adsorbed formate peaks almost on higher FT-IR than spectra 5CZrZ at almost disappeared on FT-IR spectra of A5 CZrZdisappeared at temperatures 200of the temperatures higher than 200 °C. Obviously, the dehydrogenation and reacted oxidation of on dehydrogenation and oxidation of methoxy-formaldehyde-formate sequentially rapidly sequentially reacted rapidly on A5CZrZ surface with the A5methoxy-formaldehyde-formate CZrZ surface with the presence of active oxygen. presence of active oxygen. To further confirm the effect of Au promoter, the in-situ DRIFTS spectra of CO chemisorption To further confirm the effect of Au promoter, the in-situ DRIFTS spectra of CO are shown in Figure 11 (II). CO gas displayed two peaks located at 2173 and 2115 cm−1 , respectively. chemisorption are shown in Figure 11 (II). CO gas displayed two peaks located at 2173 and 2115 When−1 CO gas adsorbed onto metal surface (COads ), rotational freedom was lost, and COads shows cm , respectively. When CO gas adsorbed onto metal surface (COads), rotational freedom was lost, only one peak. Meanwhile, only A5 CZrZ adsorbed CO at 25 ◦ C, and COads peaks were observed at and COads shows only one peak. Meanwhile, only A5CZrZ adsorbed CO at 25 °C, and COads peaks around 2110 cm−1 . The CO preferentially bonded onto Au at room temperature [64,65]. Lee et al. [66] were observed at around 2110 cm−1. The CO preferentially bonded onto Au at room temperature indicated that moveable oxygen tended to catalyze CO and in-situ 2 . Integrating ads toto [64,65]. Lee et al. [66] indicated that moveable oxygenCO tended catalyze COads to the CO2XAS . Integrating DRIFTS results, the suggested mechanism of POM reaction on A CZrZ catalyst is depicted the XAS and in-situ DRIFTS results, the suggested mechanism of 5POM reaction on A5CZrZ in Scheme dehydrogenation CH3dehydrogenation OH formed a methoxy group, which absorbedgroup, onto Cu0 catalyst1. isThe depicted in Scheme 1.ofThe of CH3OH formed a methoxy surface. moveable oxygen sequential which The absorbed onto Cu0 enhanced surface. the Theformation moveableof methoxy-formaldehyde-formate oxygen enhanced the formation of + + reaction on Cu -rich A5 CZrZ surface. Monodentate at a temperature lowerMonodentate than Ti (120 ◦ C). methoxy-formaldehyde-formate sequential reaction formed on Cu -rich A5CZrZ surface. After ignition, bidentate formate wasTiobserved, whichignition, may have decomposed The H2 O formed at a temperature lower than (120 °C). After bidentate formate quickly. was observed, and H2 were from H*quickly. and OH*, theand CO* with moveable oxygen to form which may generated have decomposed Theand H2O H2reacted were generated from H* and OH*, andCO2 . 2. These mobility the CO* reacted with moveable form COoxygen features could all prove that A5CZrZ These features all prove that the Aoxygen with good start thethe reaction at low 5 CZrZ to with good oxygen mobility could start the reaction at low temperature and lower CO selection. temperature and lower CO selection.

◦ C over Figure In-situDRIFT DRIFT spectra spectra of °C◦ C (II)(II) COCO chemisorption at 25at°C Figure 11.11.In-situ of (I) (I) POM POMreaction reactionatat125 125 chemisorption 25over 5CZrZ. CZ, CZrZ,and and(c) (c)AACZrZ. (a)(a) CZ, (b)(b) CZrZ, 5

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Scheme 1. Suggested Suggestedmechanism mechanismofof POM reaction onCZrZ A5CZrZ catalyst. * indicted as on metal on Scheme 1. POM reaction on A catalyst. * indicted as metal catalysts. 5 catalysts.

3. Materials and Methods 3.1. Preparation of Catalyst

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3. Materials and Methods 3.1. Preparation of Catalyst The catalysts of CZ (ca. Cu 30 wt.% and Zn 70 wt.%) and CZrZ (ca. Cu 30 wt.%, Zr 15 wt.% and Zn 55 wt.%) were prepared using the coprecipitation (CP) technique. The precursors of Cu(NO3 )2 ·3H2 O, ZrO(NO3 )2 ·xH2 O, and Zn(NO3 )2 ·6H2 O were dissolved in pre-heated deionized water with vigorous stirring at 70 ◦ C. The solution pH was kept to 7 by 1N Na2 CO3 for one hour, followed by filtration of the CZ and CZrZ precipitates. The precipitates were washed with 2 L of deionized water and dried at 105 ◦ C overnight. Afterwards, the catalysts were calcined in 100 mL/minute air flow at 400 ◦ C for 4 h. The catalysts of Ax CZrZ (x = 1, 3, 5 wt.% of Au, Cu 30 wt.%, Zr 15 wt.%, and Zn 55−x wt.%) and A5 CZ (ca. Au 5 wt.%, Cu 30 wt.%, and Zn 65 wt.%) were prepared using the deposition precipitation (DP) technique. The dried CZrZ and CZ catalysts were suspended in 500 mL deionized water with vigorous stirring at 70 ◦ C. The 0.01 M HAuCl4 ·3H2 O solution was added to the CZrZ and CZ solution, and kept at pH 7–7.5 for one hour by using 10% HCl solution. After filtrating, the Ax CZrZ and A5 CZ precipitates were washed with 2 L deionized water, then dried at 105 ◦ C overnight. Afterwards, the catalysts were calcined in 100 mL/minute air flow at 400 ◦ C for 4 h. 3.2. Characterization of Catalysts The ICP-MS (Perkin Elmer-SCIEX ELAN 5000, Waltham, MA, USA) was manipulated to evaluate the metallic compositions of the catalysts. XRD analysis was measured by Rigaku RINT1100 diffractometers (Tokyo, Japan) with Copper-Kα1 (λ = 1.54056 Å). The radiation scanning 2θ angle rates ranged from 25◦ to 70◦ and 3◦ /minute. The fresh catalyst reduced by 10% H2 /N2 at 250 ◦ C for 30 min before reduction state XRD measurement. The surface area of catalysts was obtained by Micromeritics ASAP-2020 (Norcross, GA, USA). The catalysts were pre-treated under vacuum at 300 ◦ C. The N2 adsorption/desorption isotherms were measured at −196 ◦ C. Surface area calculation was performed according to the Brunauer–Emmett–Teller (BET) method [67]. Raman spectra were collected by Thermo Scientific DXR Microscopy Raman (Madison, WI, USA). The excitation source was 532 nm Laser. The spectra were collected 30 times at laser power 10 mW with 5 s exposure. HR-TEM images were taken on a JEOL-2100 (Tokyo, Japan) with a LaB6 electron gun source and operated at 200 kV. The sample preparation procedures included putting 1 mg of catalyst into 2 mL ethanol, which was ultra-sonicated for 120 min to produce a well-suspended sample solution. Then, 1 mL suspended solution was deposited onto carbon-coated nickel grids. The grids with catalyst were placed into a vacuum oven at 60 ◦ C overnight to completely evaporate the ethanol. The energy-dispersive X-ray spectroscopy (EDS) was measured by Thermo Phenom ProX scanning electron microscope (SEM) equipped with EDS (EDAX, Mahwah, NJ, USA). The electron gun was a CeB6 and was operated at 15 kV. The energy resolution of EDS by silicon drift detector (SDD) at Mn Kα was less than 137 eV. The samples were grinded and mounted with conductive carbon tape for measurement. In the temperature programmed reduction (TPR) experiment, a 4 mm inner diameter U-shaped tube reactor was filled with 55 mg of catalyst. The catalyst was reduced by 10% H2 /N2 at a flow rate of 30 mL/min with a heating rate at 7 ◦ C/min from ambient temperature to 300 ◦ C, and the consumption of hydrogen was recorded by thermal couple detector (TCD). The TPR profile was deconvoluted to multiple peaks by using Origin software. Copper dispersions were analyzed by nitrous oxide chemisorption [68]. After the TPR process, the reactor was cooled to room temperature. N2 O gas in 30 mL/min of flow rate was introduced into the reactor for 30 min and then purged with N2 for 15 min. The second TPR (S-TPR) test was processed and detected by TCD. The Cu dispersion was calculated by multiplying two times of the area of S-TPR and dividing by the TPR area.

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Temperature program desorption of oxygen (O2 -TPD) was utilized to identify the oxygen adsorption-desorption ability of the catalysts. The 55 mg catalysts were pre-reduced at 250 ◦ C by 10% H2 /90% N2 mixed gas in a U-shape tube reactor for one hour and then were cooled down to room temperature in flowing He (99.9995%). After that, the catalyst was treated in O2 (99.999%) at 200 ◦ C for one hour and then was cooled down to room temperature under flowing O2 . The O2 gas was removed by flowing He for one hour. In order to ensure the saturation of O2 chemisorption on catalysts, the O2 treatment procedure was applied one more time [66]. Afterwards, the reactor temperature was raised from room temperature to 450 ◦ C at a heating rate of 7 ◦ C/min. Oxygen desorption during the heating range was determined by TCD. X-ray photoelectron spectroscopy (XPS) spectra were recorded on a photoelectron instrument via Kratos Axis Ultra DLD (Kratos Analytical Ltd, Manchester, UK) under ultra-high vacuum. The binding energies were referred to C1s line of adventitious carbon 285 eV. XAS (X-ray absorption spectroscopy) spectra, studied for the electronic states of copper catalysts, were recorded on the Wiggler beam-line at Synchrotron Radiation Research Center (SRRC), Taiwan. Absorption of Cu K-edge (8.979 KeV) measured by transmission mode was used for XANES (X-ray absorption near-edge structure) analysis, and the data was calculated by using WinXAS software (V.3.0). The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) infrared spectra were collected by Thermo Scientific Nicolet 6700 spectrometer with a MCT-A detector (Madison, WI, USA). The 100 mg catalyst was packed into the in-situ high-temperature reaction chamber, which was installed in the HARRICK diffuse reflectance accessory. The total flow gas through the in-situ cell was set at 30 mL/minute and 100 mL/minute for CO adsorption and POM reaction, respectively. The spectra scan number was 64 with a resolution of 4 cm−1 . 3.3. Catalytic Activity and Durability The freshly calcined catalysts were ground into fine powders and sieved to 60–80 mesh for catalytic activity testing, then 100 mg of catalyst was packed into a 4-mm inner diameter quartz fixed-bed reactor and reduced by 10% H2 /N2 at 250 ◦ C for 30 min before measurement. The conditions of POM experiment consisted of O2 /CH3 OH ratio was 0.5 with 60 K h−1 Gas Hourly Space Velocity (GHSV) and 9.48 h−1 Weight Hourly Space Velocity (WHSV), respectively. Meanwhile, durability was tested at 250 ◦ C for 12 h under an accelerated aging condition (60 Kh−1 of GHSV and 47.4 h−1 of WHSV). Catalytic activity analyzed by on-line GC with two TCD detectors equipped with Porapak Q (H2 , CO2 , and CO) and Molecular Sieve 5A (CO2 , H2 O, and CH3 OH) columns. The calculation equations for CH3 OH conversion (CMeOH ), H2 selectivity (SH2 ), and CO selectivity (SCO ) were as follows: CMeOH = (nMeOH,in − nMeOH,out )/nMeOH,in × 100%

(2)

SH2 = nH2 /(nH2 + nH2O ) × 100%

(3)

SCO = nCO /(nCO2 + nCO ) × 100%

(4)

4. Conclusions The poor durability of CZ catalyst was improved by the addition of ZrO2 , which prevented catalyst sintering during POM reaction. Meanwhile, the Au promoter was utilized to lower the Ti and SCO of CZrZ in POM. The deactivation rate constant of A5 CZrZ was similar to CZrZ and 1.7 times better than A5 CZ and CZ, which indicated that ZrO2 was the main factor in maintaining durability. The A5 CZrZ catalyst with better reducibility, oxygen mobility, and higher Cu+ /Cu0 ratio could lower the Ti to 120 ◦ C and showed more than 90% of CMeOH and SH2 at 125 ◦ C. It was observed with in-situ DRIFTS of A5 CZrZ that the methoxy transferred to formate at around 125 ◦ C. The methoxy-formaldehyde-formate sequence processed rapidly with more Cu+ and the presence of active oxygen. The Au promoter not only enhanced the affinity to adsorb CO but also increased moveable oxygen to react with CO on the catalyst surface. The SCO could be lowered to 6% at 200 ◦ C.

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of active active oxygen. oxygen. The The Au Au promoter promoter not not only only enhanced enhanced the the affinity affinity to to adsorb adsorb CO CO but but also also increased increased of 16 ofactive Catalysts 2018, 8,19active 345 oxygen. 16also ofincreased 19increased of The Au promoter not only enhanced the affinity to adsorb CO but also of oxygen. The Au promoter not only enhanced the affinity to adsorb CO but moveable oxygen oxygen to to react react with with CO CO on on the the catalyst catalyst surface. surface. The The SSCO CO could could be be lowered lowered to to 6% 6% at 200 200 moveable at moveable oxygen to to react with CO onon the catalyst surface. The SCOSCO could bebe lowered to to 6%6% at at 200 moveable oxygen react with CO catalyst surface. The could lowered 200 °C.CO Based on these these features, the AxxCZrZ CZrZ catalyst produced good catalytic performance, reduced °C. Based features, the A catalyst produced aathe good catalytic performance, reduced to adsorb but on also increased °C. Based on these features, the A x CZrZ catalyst produced a good catalytic performance, reduced °C. Basedand on the these features, the Aproduced xCZrZ catalyst produced a good catalytic performance, Scolowered and ignition ignition temperature, and stillAmaintained maintained good durability in POM POM reaction. and temperature, still good durability in reaction. Based a good catalytic performance, reduced Sco and reduced O could Sco be to 6%on atthese 200 features, x CZrZ catalyst Sco and ignition temperature, and still maintained good durability in in POM reaction. Sco and ignition temperature, and still maintained good durability POM reaction. ignition temperature, and still maintained good durability in POM reaction. catalytic performance, reduced Catalysts 2018, 8, x FOR PEER REVIEW 16 ofof 19methanol (CMeOH), ( Figure 1. Temperature of catalyst performance: conversion Supplementary Materials: The following following are are available available online at atprofiles www.mdpi.com/xxx/s1, Figure(a)S1: S1: Supplementary Materials: The online www.mdpi.com/xxx/s1, Figure in POM reaction. Supplementary Materials: The following are(SH2 available online of atcarbon www.mdpi.com/xxx/s1, Figure S1: (■) CZ, ( selectivity of hydrogen ), (c) selectivity monoxide (SCO) in POM reaction.

Supplementary Materials: The following are available at for www.mdpi.com/xxx/s1, Figure S1: Deactivation rate in in POM POM reaction: (■)The CZ, (●) CZrZ, CZrZ, (★) Au55CZrZ, CZrZ, andat(◊) (◊) Au55CZ CZonline at 250 250 °C °C for 12 hh in in an an Deactivation rate reaction: (■) CZ, (●) (★) Au and Au at 12 Supplementary Materials: following are available online http://www.mdpi.com/2073-4344/8/9/345/s1, ◦C of active oxygen. The Au promoter not only enhanced the affinity to adsorb CO but also increased −1 Deactivation rate in POM reaction: (■) CZ, (●) CZrZ, (★) Au 5CZrZ, and (◊) Au 5CZ at 250 °C for 12 h in anSpace −1 −1 −1 −1 CZrZ, (▲) A 1 CZrZ, (▼) A 3 CZrZ, (★) A 5 (◊) A 5 CZ at 60 Kh Gas Hourly Veloc Deactivation rate in POM reaction: (■) (●) CZrZ, (★) Au 5 CZrZ, and (◊) Au 5 CZ at 250 °C for 12 h in an Figure S1: Deactivation rate in POM reaction: (  ) CZ, ( ) ( ) CZrZ, and ( ) Au CZ at 250 for accelerated aging aging condition condition (60 (60 Kh Kh of of GHSV GHSV and and 47.4 47.4 hh of of WHSV). WHSV). Figure Figure S2: S2: XRD XRD profiles of of different different accelerated 5 profiles 5 www.mdpi.com/xxx/s1,moveable Figure S1: −1−of −1 − 1−1 of 1 of −1 accelerated aging condition (60 Kh GHSV and 47.4 h of WHSV). Figure S2: XRD profiles of different −1 oxygen to react with CO on the catalyst surface. The S CO could be lowered to 6% at 200 12 h in an accelerated aging condition (60 Kh GHSV and 47.4 h WHSV). S2: XRD profiles of accelerated aging condition (60 Kh of GHSV and 47.4 h WHSV). Figure profiles of different and h Weight Hourly Space (WHSV) with O2/MeOH = 0.5. catalysts (reduction (reduction state): state): (a) (a) CZ, CZ, (b) (b) CZrZ, CZrZ, (c) (c)(GHSV) A11CZrZ, CZrZ, (d)9.48 A33CZrZ, CZrZ, and (e) (e) A55CZrZ. CZrZ. (◊)Velocity Cu, (●) (●) ZnO. ZnO. Figure catalysts A (d) A and A (◊) Cu, Figure (◊) Au5CZ at 250 °Cdifferent for 12 hcatalysts in an (reduction Figure 3. XRD profiles of freshand catalysts: (a) CuO, (b) (●) (c)Figure CZ, (d) CZrZ, (e catalysts (reduction state): (a)A(a) CZ, (b) CZrZ, (c)A A 1CZrZ, CZrZ, (d)a°C, A CZrZ, (e) A 5CZrZ. CZrZ. Cu, state): (a) CZ, (b) CZrZ, (d) A (e) A ((◊) ♦)(◊) (ZnO, )(●) ZnO. 1°C, 33CZrZ, 5(◆) °C. of Based on these features, the xfor CZrZ catalyst produced good catalytic performance, reduced catalysts (reduction state): CZ, (c) A(b) 1(b) CZrZ, (d) A 3CZrZ, and (e) A5CZrZ. Cu, ZnO. Figure S3: XRD XRD profiles profiles of CZrZ catalysts after calcination calcination for atCZrZ, (a)(c) 400 550 °C, and (c)and 750 °C. (◆) CuO, S3: CZrZ catalysts after 44 hh(b) at (a) 400 °C, 550 and (c) 750 °C. CuO, ◦ ◦ ◦ gure S2: XRD profiles of different A 3 CZrZ, and (g) A 5 CZrZ. ( ◆ ) CuO ( Figure S3: XRD profiles of CZrZ catalysts after calcination for 4 h at (a) 400 C, (b) 550 C, and (c) 750 C. ( ) CuO, S3: XRD profiles of CZrZ catalysts after calcination for 4 h at (a) 400 °C, (b) 550 °C, and (c) 750 °C. (◆) CuO, S3: XRD profiles of CZrZ catalysts after calcination for 4 h at (a) 400 °C, (b) 550 °C, and (c) 750 °C. (◆) CuO, (●) ZnO, ZnO, (o) (o) ZrO ZrO -tetragonal, (□)temperature, ZrO22-monoclinic. -monoclinic. Figure S4: Raman Raman good spectra of (a) (a) CZ, CZ,in and (b) CZrZ. CZrZ. Table Sco22-tetragonal, and ignition and Figure still maintained durability POM reaction. (●) (□) ZrO S4: spectra of and (b) Table (e) A5CZrZ. (◊) Cu, (●) ZnO. (o) Figure ( ) ZnO, ZrO -tetragonal, (  ) ZrO monoclinic. Figure S4: Raman spectra of (a) CZ, and (b) CZrZ. Table S1: 2 (o)(o) 2 (□)(□) (●)(●) ZnO, ZrO 2-tetragonal, 2-monoclinic. Figure S4: Raman spectra of of (a)(a) CZ, and (b)(b) CZrZ. Table ZnO, ZrO 2-tetragonal, ZrO 2-monoclinic. Figure S4: Raman spectra CZ, and CZrZ. Table S1: Composition Composition of catalyst catalyst surfaces measured by EDS EDSZrO (%). Figure S5: The EDS element mapping profile: (a) S1: of surfaces measured by (%). Figure The EDS element profile: (a) Composition of catalyst surfaces measured by EDS (%).S5: Figure S5: The EDSmapping element mapping profile: (a) CZ, b) 550 °C, and (c) 750 °C. (◆)S1: CuO, Composition of catalyst surfaces measured by EDS (%). Figure S5: The EDS element mapping profile: (a)(a) ◦ S1: Composition of catalyst surfaces measured by EDS (%). Figure S5: The EDS element mapping profile: CZ, (b) (b) CZrZ, CZrZ, (c) A A11CZrZ, CZrZ, (d) A A33CZrZ, CZrZ, and (e) A55(e) CZrZ. Figure S6: Mole Mole fractions ofwww.mdpi.com/xxx/s1, carbon components at atFigure Materials: The following are Figure available online atof CZ, (c) (d) and (e) A CZrZ. Figure S6: fractions carbon components at (b)Supplementary CZrZ, (c) A1 CZrZ, (d) A3 CZrZ, and A5 CZrZ. S6: Mole fractions of carbon components 250 C S1: for ctra of (a) CZ, and (b) CZrZ. CZ, Table (b) CZrZ, (c) A 1 CZrZ, (d) A 3 CZrZ, and (e) A 5 CZrZ. Figure S6: Mole fractions of carbon components at at CZ,rate (b) CZrZ, (c) A1CZrZ,(■) A3CZrZ, and (e) A 5CZrZ. Figure S6:Au Mole offor carbon components 250 °C °C for for 12 12 hhin in an accelerated condition: CO, CO 2,,,(▲) (▲) MeOHout, Carbon balance. (a)CZ, CZ, 250 condition: (●) 22 () balance. (a) CZ, inaging POM reaction: CZ, (●) CZrZ, Au 5CZrZ, and (◊) 5CZfractions at 250 °C 12 h in an 12hDeactivation inan anaccelerated aging condition: ((■) (d) )CO, ( )CO ( (★) ) MeOHout, MeOHout, (() ) Carbon balance. (a) (b) CZrZ, and e EDS element mapping profile: (a) 250 °C for 12 h in an accelerated aging condition: (■) CO, (●) CO 2 , (▲) MeOHout, () Carbon balance. (a) CZ, −1 −1 (c)accelerated A Figure S7: XPS of an Au (BE 82–97 ev) (Fresh): A1(a) CZrZ, (b) A2,3(b) CZrZ, and (c) A() lines (a) CZ, 250 °C for 12 in accelerated aging condition: CO, CO (▲) MeOHout, balance. (b) CZrZ, CZrZ, and and (c) A55CZrZ. CZrZ. Figure S7:hXPS XPS of Au (BE in 82–97 ev) (Fresh): (a) A(●) CZrZ, (b) A CZrZ, and (c)Carbon (b) (c) A Figure S7: of 4f4f in (BE in 82–97 ev) (Fresh): A 11CZrZ, A 33CZrZ, and (c) aging condition (60 Kh of GHSV and 47.4 h(a)(■) of WHSV). Figure S2: XRD profiles of(blue different 5 CZrZ. 5 CZrZ 4fAu fractions of carbon components at 0 ; green 3+in (b) CZrZ, (c) A 5CZrZ. Figure S7:(c) XPS ofBE Auin 4f Au (BE 82–97 (Fresh): AXPS 1A CZrZ, (b) A3Figure CZrZ, (c)(c) 3+ev) 00;; green 3+ arecatalysts assigned to BE inand Au lines are assigned to ) in and Figure S8: XPS(a) of Au (BE 82–97 ev): and (b) CZrZ, and (c) A 5CZ, CZrZ. Figure S7: of Au 4fA (BE 82–97 ev) (Fresh): (a) (b) A3CZrZ, and A55CZrZ CZrZ (blue (blue lines are assigned to BE in Au green lines are to BE in Au and Figure S8: XPS of in 4f1CZrZ, A lines are assigned to BE in Au lines are assigned to BE Au )) and S8: of (reduction state): (a) (b) CZrZ, AXPS 1assigned CZrZ, (d) 3CZrZ, and (e) AFigure 5CZrZ. (◊) Cu, (●) ZnO. OHout, () Carbon (a) balance. (a) CZ, 0; green 3+) 3+ ◦ Clines 0 ; XPS of 0 A 5CZrZ (blue lines are assigned to BE in Au are assigned to BE in Au and Figure S8: A CZrZ, (b) A CZrZ, and (c) A CZrZ, after POM at 250 for 24 h. (Blue lines are assigned to BE in Au A5A CZrZ are 5assigned BE inafter Au 4;POM green are assigned toand BElines in and Figure 3 of(blue Au4f4f (BE (BE in in 82–97 82–97 ev): (a) (a) A11CZrZ, CZrZ, (b)lines Acatalysts CZrZ, and (c)calcination Ato CZrZ, after POM atlines 250 °C °C for for 24 h.°C, (Blue lines are)°C. Au ev): (b) A 33CZrZ, and (c) A 55CZrZ, at 250 (Blue are S3:1XRD profiles CZrZ after for h at (a) 400 °C, (b)24 550h. (c) Au 750 (◆) CuO,S8: XPS of h): (a) A1CZrZ, (b) Agreen 3CZrZ, and (c) 3+1). 4f (BE in 82–97 ev): (a) A CZrZ, (b)3+ A 3A CZrZ, and (c)(c) A5CZrZ, after POM atCZ, 250250 °C°C for 24 h. h. (Blue lines areare lines assigned toassigned BE in Au(a) 0; are 3+ 0Au Au 4f (BE in 82–97 ev): A 12CZrZ, (b) 3CZrZ, and A 5CZrZ, after POM at for 24 (Blue lines assigned to BE in Au green lines are assigned to BE in Au ) assigned to BE in Au ; green lines are to BE in Au ) (●) ZnO, (o) ZrO 2 -tetragonal, (□) ZrO -monoclinic. Figure S4: Raman spectra of (a) and (b) CZrZ. Table BE in Au3+) and Figure S8: XPS of to BE in Au0; green 3+) 3+ 0 assigned lines are assigned to BE in Au assigned BE in Au ; green lines assigned to and BE inrevised Au S1: Composition of to catalyst surfaces measured by EDS (%). Figure S5:)The element mapping profile: (a) Y.-J.H. coordinated theare whole study thisEDS manuscript. H.-Y.H. and H.-I.C. Author Contributions: M at 250 Author °C for 24 h. (Blue lines Y.-J.H. are Author Contributions: Y.-J.H. coordinated coordinated the the whole whole study study and and revised revised this this manuscript. manuscript. H.-Y.H. H.-Y.H. and and H.-I.C. H.-I.C. Contributions: prepared processed the experiment. H.-Y.H. analyzed XRD, IR, XPS, and XANES data, and H.-I.C. measured CZ, (b) and CZrZ, (c) A 1 CZrZ, (d) A 3 CZrZ, and (e) A 5 CZrZ. Figure S6: Mole fractions of carbon components atand Author Y.-J.H. coordinated thethe whole study and revised this manuscript. H.-Y.H. and H.-I.C. Author Contributions: Y.-J.H. coordinated study and revised this manuscript. H.-Y.H. H.-I.C. prepared and and processed theContributions: experiment. H.-Y.H. analyzed XRD, IR,whole XPS, and XANES data, and H.-I.C.H.-Y.H. prepared processed the experiment. H.-Y.H. analyzed XRD, IR, XPS, XANES data, and H.-I.C. the250 physicochemical properties of aging the catalysts and calculated the2and deactivation rates constant. wrote °C for 12 h in an accelerated condition: (■) CO, (●) CO , (▲) MeOHout, () Carbon balance. (a) CZ, prepared and processed the experiment. H.-Y.H. analyzed XRD, IR, XPS, and XANES data, and H.-I.C. prepared and processed the experiment. H.-Y.H. analyzed XRD, IR, XPS, and XANES data, and H.-I.C. measured the the physicochemical properties of of the the catalysts catalysts and and calculated calculated the the deactivation deactivation rates rates constant. constant. measured properties thisphysicochemical manuscript. his manuscript. H.-Y.H. H.-I.C. (b)and CZrZ, and (c) A 5CZrZ. Figure S7: XPS of Au4f (BE inthe 82–97 ev) (Fresh): (a) A1CZrZ, (b)deactivation A3CZrZ, rates and (c) measured the physicochemical properties of of the catalysts and calculated thethe deactivation constant. measured the physicochemical properties catalysts and calculated rates constant. H.-Y.H. wrote wrote this this manuscript. manuscript. H.-Y.H. 0; green lines are assigned to BE in Au3+) and Figure S8: XPS of Funding: This research received no external funding. PS, and XANES data, A5and CZrZH.-I.C. (blue lines are assigned to BE in Au H.-Y.H. wrote this manuscript. H.-Y.H. wrote this manuscript. ed the deactivation rates Funding: This This research received no external external funding. Funding: research no funding. Au 4f constant. (BE inreceived 82–97 ev): (a) A1CZrZ, (b) A3CZrZ, andfinancial (c) A5CZrZ, afterofPOM at 250from °C for h. (Blueoflines are The authors are grateful for the support this work the24 Ministry Science Acknowledgments: Funding: This received nono external funding. 0; research 3+) Funding: research received external funding. assigned to BEof inTaiwan. AuThis green lines are assigned to BE in Au and Technology Conversion of methanol a function of time-on-stream of POM reaction over (■) CZ Acknowledgments: The The authors authors are are grateful gratefulFigure for the the2.financial financial support of this this as work from the the Ministry of of Acknowledgments: for support of work from Ministry Acknowledgments: The authors are grateful for the financial support of this work from Ministry of of (60 Kh−1 Acknowledgments: The authors are grateful for the financial support of this work from the Ministry Interest: The Y.-J.H. authorscoordinated declare no,(★) conflict of interest. (●) CZrZ 5CZrZ, and (◊) 5CZ at 250 for 12 h in an accelerated aging condition Science and andConflicts Technology of Taiwan. Taiwan. Science Technology of Author of Contributions: theAwhole study andArevised this°C manuscript. H.-Y.H. andthe H.-I.C. Science and Technology of Taiwan. −1 Science and Technology of Taiwan. GHSV andH.-Y.H. 47.4 h of WHSV).XRD, IR, XPS, and XANES data, and H.-I.C. prepared and processed the experiment. analyzed of this work fromof Ministry Conflicts ofthe Interest: Theofauthors authors declare declare no noconflict conflict of of interest. interest. Conflicts Interest: The measured the physicochemical properties of the catalysts and calculated References Conflicts of Interest: The authors declare no conflict of of interest. Conflicts of Interest: The authors declare no conflict interest. the deactivation rates constant. H.-Y.H. wrote this manuscript. Although the above behaviors were observed, the interactions between Au particles a References References Alejo, L.; Lago, R.; Peña, M.A.; Fierro, J.L.G. Partial oxidation of methanol to produce hydrogen over 1. CZrZno might significantly affect catalytic performance and should be explored. For these pu References References Funding: This research received external CnZn-based catalysts. Appl. Catal. 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